Field of the Disclosure
The present disclosure relates to a milling cutter with which a machined surface having a high degree of surface accuracy is obtained and to a machining method using the milling cutter.
Background of the Disclosure
Grinding has been generally known as a machining method capable of finishing a machined surface of a workpiece with high accuracy in terms of surface accuracy such as surface roughness. However, in recent years, intensive studies have been made for obtaining a surface accuracy equivalent to that obtained by grinding by machining using a milling cutter, that is, by milling, for the purpose of shortening machining time.
Meanwhile, a problem has been pointed out that, in a case where a cast iron is cut by normal milling, graphite exposed on a machined surface falls down during cutting and recesses are formed at the portions where the graphite has been present, and the recesses prevent obtaining a desired accuracy in terms of surface roughness.
Accordingly, in order to solve this problem, there has been proposed a machining method, as disclosed in Japanese Unexamined Patent Application Publication No. 2007-319990, as a milling method capable of finishing a workpiece surface with high accuracy in terms of surface roughness, though the machining method is for a case where the workpiece is a spherical graphite cast iron.
This machining method is a cutting method in which a surface of a spherical graphite cast iron is modified by causing at least one tool having a major cutting edge and a minor cutting edge to cut into the surface of the spherical graphite cast iron and relatively moving the tool and the spherical graphite cast iron. In this method, the speed of the relative movement of the tool and the spherical graphite cast iron (cutting speed) is set at 600 m/min or more and graphite on the surface of the spherical graphite cast iron is covered with a matrix structure surrounding the graphite. According to this machining method, when the cutting speed is set at 600 m/min or more, plastic flow occurs in a surface layer of the matrix structure of the spherical graphite cast iron, and the graphite is covered with a layer of the matrix structure plastic flow. Therefore, although the surface of the graphite cast iron is still slightly rough, local formation of an extremely low recessed portion is prevented, and therefore a machined surface equivalent to a polished surface obtained by grinding is achieved.